Electrical interconnection systems commonly incorporate vias, or plated through holes, to make electromechanical connections between electrical components and printed circuit boards. However, via can cause significant harm to signal integrity. FIG. 1 illustrates a prior-art electrical connector system in which the electrical connector 101 attaches to a printed circuit board 102, which contains multiple layers 103. A conductive pins 104 are inserted into a plated through holes 105, which consists of a hole 106, drilled through the printed circuit board, and an annular pad 107—both of which are plated with a conductive material. The plated through holes make electrical connections between the conductive pins 104 and signal traces 108 that may be located one or more layers within the printed circuit board. The plated through holes 105 and the annular pads 107 may both act capacitively and harm signal integrity.
Often electromechanical interconnection devices incorporate resilient or spring structures to maintain contact force at the point of connection between electrical components. Different spring conductors may be compared for their ability to produce deflection for the same force applied to the resilient structures used to create the spring effect. Spring conductor structures are generally designed to: (1) establish and maintain sufficient mechanical contact force for the intended application; (2) require the smallest amount of deflection to attain this contact force; (3) have little or no permanent deformation; and (4) require the smallest volume possible.
To address each of these attributes, spring structures are often complicated in nature and difficult to manufacture, particularly when the structures are very small. Complexity of resilient interconnection structures typically increases when electrical components are disposed at various angles to each other, often necessitating curved or irregularly shaped interconnection structures. Bends and twists in conductive elements can degrade signal integrity and increase cost.
FIG. 2 illustrates the prior art of an edge card connector mounted on a mother board. The connector accepts a vertically oriented plug-in card 201 that bends the conductors 202 to produce contact force and establish electrical continuity. The conductors 202 are cantilever beams whose fixed ends 203 are attached to the horizontally oriented substrate 204. The contact forces, which are at the free ends 205 of the cantilever beams, bend the cantilever beams. Cantilever beams do not store energy in a uniform manner throughout their length. The greatest stresses or stored energy per unit volume is at the fixed end 203 of the cantilever beam and are at their lowest at the free ends 205 where the electrical contacts exist. The conductors 202 could be made smaller if they were designed to store energy more uniformly throughout the conductors' volume.
FIG. 3 illustrates prior art wherein cantilever-beam conductors 301 are disposed in an electrical connector at an angle to electrical contact pads 302 on a printed circuit board 303, which is perpendicular to printed circuit board 303 (not pictured at right). The ends or electrical contacts 304 of the cantilever-beam conductors 301 bend to produce contact force between the cantilever-beam conductors 301 and the substrate's electrical contact pad 302.
FIG. 4 illustrates another view of the prior art connector in FIG. 3, illustrating the movement of the cantilever-beam conductors, which requires air voids or gaps 405 within the normally uniform dielectric material forming the transmission line structure. The gaps or air voids 405 constitutes a physical discontinuity reducing the signal integrity of the interconnection. The air voids 405 can be compensated for by adjusting the properties and shape of the other connector parts, but this increases the complexity and cost of the connector. In addition, in FIG. 4, the conductors 301 must bend sufficiently within the air voids 405 to attain the configuration necessary for the correct characteristic or differential impedance. Because the connector's electrical contacts 304 may not mate with the electrical contact pads 302 in a consistent manner, the cantilever-beam conductor's movement may alter the spatial and dimensional requirements necessary to provide the correct characteristic or differential impedance and this alteration may reduce signal integrity.
FIG. 5 illustrates a typical prior art torsion bar conductor. A torsion bar conductor 501 with head 505 is inserted into a two-tined receptacle 502, which exerts a twisting force on the head 505, which twists the torsion bar conductor 501. A high speed signal will encounter sharp corners 504 on the torsion bar conductor 501 creating signal reflections. The tines 503 on receptacle 502 are capacitive stubs. Both the signal reflections and the capacitive stubs reduce signal integrity.
FIG. 6 illustrates a prior art cantilever beam commonly used to create force in electrical interconnection systems. FIG. 6 illustrates a round wire beam 601 of length L, radius r and modulus of elasticity E. It has a fixed section 602 and has a force 603, FC, placed at the unconstrained tip section 604 (which is a moment arm). The force is in a direction perpendicular to the cantilever round wire beam's axis.
Despite these and other efforts in the art, further improvement in cost and performance is possible by simplifying design and lowering manufacturing cost. There is opportunity and need for improvements which will address the gap between present options and future requirements.